The present invention relates to a melt or solution processable polyaniline and processes for the preparation of said melt or solution processable polyaniline by using novel dopants synthesised from inexpensive, naturally occurring bimonomers from cashew nut shell liquid. The present invention also relates to a novel process for the preparation of dopants for use in the present invention. The novel dopants employed in the process of the present invention are sulphonic acid derivatives of hydrogenated cardanol (3-pentadecyl phenol), methyl ether of 3-pentadecyl phenol (3-pentadecyl anisol) and phenoxy acetic acid of 3-pentadecyl phenol of the formulae 1, 2 and 3 shown below: 
The doping of polyaniline with the dopants described above imparts conductivity to polyaniline and polyaniline doped with these dopants can be used in applications to develop transparent highly conductive films and coatings. Polyaniline which is brittle and unprocessable could be processed by melt or solution techniques by protonating with these functionalized dopants. These conductive polymers show a tremendous promise for industrial applications ranging from electrostatic dissipation to electrochromic displays such as the use in antistatic ESD coatings, absorption of radar frequencies, corrosion prevention, EMI/RFI shielding, electrochemical actuators, lithographic resists, lightning protection, microelectronics, polymer electrolytes, photovoltaics, rechargeable batteries, smart windows, solar cells, bio-sensors etc. One of the significant features of the structure of the dopant prepared by the process of the present invention is that it has a flexible n-alkyl (C15H31) substituent in the meta position of the aromatic ring which makes the doped polyaniline melt processable and render high solubility for polyaniline in common solvents. The presence of hydrophobic and hydrophilic moieties in the same molecule imparts the polyaniline dopant combination compatibility with a large spectrum of polymers for probing applications involving polymer blends. This enhanced solubility of doped polyaniline makes it possible for the preparation of highly transparent and conductive films and coatings by solution casting or melt processing techniques and conductive plastics could be prepared by blending the doped polyaniline with classical thermoplastic polymers. Thus, these conductive polymers show vast promise for industrial applications such as in static films for transparent packaging of electronic components, electromagnetic shielding, rechargeable batteries, light emitting diodes, non-linear optical devices, sensors for medicine and pharmaceutics and membranes for separation of gas mixtures. The industries to which this invention can be applied are electronic industries, plastics industries, medical industries etc.
Polyaniline is one of the most promising conductive polymers due to its uncomplicated polymerisation and excellent chemical stability combined with relatively high levels of conductivity (J. C. Chiang and A. G. Mac Diarmid, synth. Met., 13, 193 (1986). However, it is highly intractable and infusible because of its aromatic nature, the interchain hydrogen bondings and the charge delocalization effects. Emeraldine base form of polyaniline is soluble only in N-methyl-pyrrolidone, selected amines, concentrated sulfuric acid and other strong acids [M. Angelopoulos, A. Ray, A. G. Mac Diarmid and A. J. Epstein, Synth. Met., 21, 21 (1987); X. Tan, Y. Sun, Y. Wei, Makromol. Chem. Rapid Commun. 9, 829 (1988); M. Angelopoulos, G. E. Asturias, S. P. Ermer, A. Ray, E. M. Sherr, A. G. Mac Diarmid, M. A. Akhtar, Z. Kiss and A. J. Epstein, Mol. Cryst Liq. Cryst 160, 151 (1988); A. Andreatta, Y. Cao, J. C. Chiang, A. J. Heeger, P. Smith, Synth. Met. 26, 383 (1988)]. Emeraldine salt is even more intractable. Covalent substitution such as N-alkylation improves melt processability and solubility in various solvents (W. Y. Zheng, K. Levon, J. Laakso, J. E. Osterholm Macromolecules, 27, 7754 (1994). Recently, it was reported that by using functionalised dopants the melt and solution processability of polyaniline can be increased (Y. Cao, P. Smith and A. J. Heeger, Synth. Met., 48, 91 (1992), Y. Cao, P. Smith and A. J. Heeger, PCT Patent Application WO 22/22911, 1992, Y. Cao, P. Smith, Polymer, 34, 3139 (1993), T. Karna, J. Laakso, E. Savolainen, K. Levon European Patent Application EP 0 545 729 A1, (1993) K. Levon, K. H. Ho, W. Y. Zheng, J. Laakso, T. Karna, T. Taka, J. E. Osterholm, Polymer, 36,2733(1995)., C. Y. Yang, Y. Cao, P. Smith and A. J. Heeger synth. Met. 53,293(1993). A. Pron, J. Laakso, J. E. Osterholm and P. Smith Polymer34, 4235(1993), J. Laakso, A. Pron and S. Lefrant J. Polym. Sci. Part A: Polym. Chem. 33, 1437(1995).
Specific functionalised dopants render high solubility for polyaniline into common solvents and can be solution processed from these solvents by solution casting method. Here, the counterions of the dopant simultaneously act as surfactants for bulk polymers or organic solvents. Well known examples of such counterions are p-dodecylbenzenesulfonic acid and camphor sulphonic acid. The solubilizing group can be introduced to the polymer as an inherent part of the dopant while its acidic center protonates it. According to Heeger et al., the m-cresol solution of polyaniline-camphor sulphonic acid allow preparation of films having d.c conductivities up to 400 S/cm. However, m-cresol is suspected to be a cancer causing substance, thus rendering this route instantly undesirable for obtaining soluble, doped PANI (polyaniline) on a large scale.
The main disadvantage of conductive polyaniline is its limited thermal processability. However, from the industrial point of view, the fabrication of a thermally processable conducting polymer would be preferable because it should exhibit appropriate rheological parameters in the temperature range typically used for classical polymer processing (140-220xc2x0 C.) and it should be thermally processable. No meaningful conductivity decrease should be observed at the processing temperature. Also, the doping should be carried out in situ during processing. Polymers are usually thermally processed in their molten state or plasticized state. The fabrication of a conducting polymer, which would melt in its doped state, is of course, extremely difficult. Many of alkyl or aryl diesters of phosphoric acid induce simultaneous plastification leading to thermal processability of polyaniline.
The main object of the present invention is, therefore, to provide a process of preparation of melt/solution processable polyaniline by using sulphonic acid dopants synthesized from 3-pentadecyl phenol, which is hydrogenated cardanol.
Another object of the invention is to provide a process for the synthesis of protonated polyaniline by using these dopants and to obtain highly conducting freestanding flexible films and coatings of polyaniline with thermoplastic polymers.
The sulphonic acid derivatives of 3-pentadecyl phenol which is otherwise known as hydrogenated cardanol, having a long aliphatic hydrocarbon side chain (C15H31) in the meta position of the aromatic ring, have not been reported to be used as protonating-plasticizing dopants. The introduction of the dopant having the hydrophobic group not only enhances the conductivity of polyaniline but also causes its solubilization and plastification. The doped polymer can, therefore, be thermally or solution processed. There is no report that a sulphonic acid system renders the polyaniline thermally processable. Free standing flexible films could be prepared by the hot pressing method and it exhibits a maximum conductivity value of 40 S/cm. Cardanol is a distillation product of an inexpensive natural material known as cashew nut shell liquid. Cardanol with its long flexible aliphatic side chain has special structural features for chemical modification into functionalised dopants to obtain plasticized polyaniline.
The main finding underlying the present invention is that the dopants synthesized by sulphonation of 3-pentadecyl phenol, methyl ether of three pentadecyl phenol and phenoxy acetic acid of pentadecyl phenol, have been found to plasticize and protonate the polyaniline. By hot pressing method, free standing flexible films of doped polyaniline could be prepared and these films are thermally stable at processing temperatures up to 200xc2x0 C. The other main finding underlying the present invention is that these dopants have hydrophobic groups, which enable them to act as an emulsifying cum protonating agent. Thus, in situ emulsion polymerisation of polyaniline could be carried out to obtain high molecular weight polyaniline. Another finding underlying the present invention is that flexible conductive plastic films can be prepared by the hot pressing of polyblend of protonated polyaniline and classical thermoplastics such as poly(vinyl chloride), poly(methyl methacrylate), poly(vinyl alcohol) etc. and classical elastomers such as natural rubber, ethylene vinyl acetate copolymer etc.
The present invention provides a process for the synthesis of conductive composites of protonated polyaniline with classical thermoplastic polymer such as polyvinyl chloride and classical elastomeric polymer such as ethylene vinyl acetate copolymer with a very low percolation threshold, especially with polyvinyl chloride.
The percolation threshold in polyaniline based conducting composites is of crucial importance for at least two reasons: (a) due to the rather high extinction coefficients of polyaniline for the blue and red light, highly transparent, green films can be fabricated only at extremely low contents of this polymer in the composite and (b) mechanical properties characteristic of the host insulating polymer can be retained only for a small content of the conductive polymer in the composite. These requirements are fulfilled in the polyblend of protonated polyaniline and polyvinyl chloride because the conductive phase exhibits a special morphology of the self-assembled, interpenetrating polymer network type and hence flexible conductive plastic films can be prepared by the hot pressing of polyblend of protonated polyaniline and polyvinyl chloride.
The process of the present invention has essentially the following steps: 1) preparation of the dopants by synthesis involving sulphonation of 3-pentadecyl phenol, methyl ether of 3-pentadecyl phenol and phenoxy acetic acid of pentadecyl phenol, 2) doping by mechanical mixing or by in situ doping emulsion polymerisation of aniline in the presence of the dopants, 3) preparation of the doped polyaniline films by solution and/or melt processing methods and 4) blending of protonated polyaniline with thermoplastics such as poly(vinyl chloride), poly(methylmethacrylate), poly(vinyl alcohol), poly(vinyl acetate) and elastomers such as ethylene vinyl acetate copolymer, natural rubber etc.
The present invention provides a melt or solution processable polyaniline, which comprises of polyaniline doped with one or more dopants selected from the compounds of the formulae: 
said melt or solution processable polyaniline having the following characteristics:
(a) conductivity ranging between 3 to 60 S/cm.
(b) high solubility in weak polar or non polar solvents selected from chloroform; tetrahydrofuran, xylene, m-cresol
(c) thermal stability up to 200xc2x0 C.
(d) three dimensional variable range doping condition in the range of 150 to 50 K high degree of crystalline order.
The present invention also provides process for the preparation of melt/solution processable polyaniline by protonating with one or more dopants selected from the compounds of formulae (1), formula (2) and formula (3) 
which comprises synthesising said dopants by sulphonation of 3-pentadecyl phenol, methyl ether of 3-pentadecyl phenol and phenoxy acetic acid of 3-pentadecyl phenol, protonating aniline by mechanical mixing or by in situ doping emulsion polymerisation of aniline with one or more of said dopants to obtain protonated polyaniline, subjecting the product so obtained to conventional solution and/or melt processing methods to obtain said melt/solution processable polyaniline.
If desired, said melt/solution processable polyaniline may be with thermoplastics or elastomers to obtain the conductive blends of protonated polyaniline.
Thus, the present invention also provides a process for the preparation conductive blends of protonated polyaniline by protonating with one or more dopants selected from the compounds of the formulae (1), formula (2) and formula (3) 
which comprises synthesising said dopants by sulphonation of 3-pentadecyl phenol, methyl ether of 3-pentadecyl phenol and phenoxy acetic acid of 3-pentadecyl phenol, protonating aniline by mechanical mixing or by in, situ doping emulsion polymerisation of aniline with one or more of said dopants to obtain protonated polyaniline, subjecting the product so obtained to conventional solution and/or melt processing methods to obtain said melt/solution processable polyaniline and blending said melt/solution processable polyaniline with thermoplastics or elastomers to obtain said conductive blends of protonated polyaniline.
The thermoplastic may be selected from poly(vinyl chloride), poly(methylmethacrylate), poly(vinyl alcohol) and poly(vinyl acetate) and said elastomers is selected from such ethylene vinyl acetate copolymer and natural rubber.
In a preferred embodiment, the protonation was carried out either by mechanical mixing or by in situ doping emulsion polymerisation route.
In another preferred embodiment said plasticization of polyaniline is carried out simultaneously during the process of protonation.
In yet another preferred embodiment said doped polyaniline films are prepared but solution casting in the presence of solvents selected from CHCl3, THF and xylene.
In another preferred embodiment said doped polyaniline films have an electrical conductivity in the range 3-60 S/cm and are prepared by hot pressing in a hot press by using the conventional melt processing technique.
In a yet another embodiment of the present invention the dopant sulphonic acid of 3-pentadecyl phenol, sulphonic acid of 3-pentadecyl anisole and sulphonic acid of 3-pentadecylphenoxy acetic acid are synthesized from 3-pentadecyl phenol, which is obtained by hydrogenation of cardanol, (distilled product of cashew nut shell liquid, an inexpensive naturally existing biomonomer).
In a further embodiment of the present invention sulphonation of 3-pentadecyl phenol and the derivatives of 3-pentadecyl phenol was carried out at 100-120xc2x0 C. by using 98% of conc. sulphuric acid. The method of sulphonation of 3-pentadecyl phenol has been reported by S. C. Sethi., B. C. Subba Rao, S. B. Kulkarni, S. S. Katti, Ind. J. Tech., 1, 348, (1963) and M. T. Harvey, U.S. Pat. No. 2,324,300 (to Harvel corp.) 1943, Chem. Abstr., 38 (1944) 188; U.S. Pat. No. 2,137,607 (to Harvel corp.) 1943, Chem. Abstr. 37,5806, (1943); U.S. Pat. No. 2,377,552 (to Harvel corp.) 1945, Chem. Abstr., 39, 4245 (1945) earlier. However, there is no report on its use as a functionalised dopant for polyaniline.
In still another embodiment of the present invention polymerisation of aniline was carried out in aqueous medium at 0xc2x0 C. by using ammonium persulphate as the oxidant.
In yet another embodiment of the present invention, the in situ emulsion polymerisation of PANI was carried out at 0xc2x0 C. by using the solvent s xylene or chloroform.
In yet another embodiment free standing flexible films could be prepared both by melt/solution processing by using solvents chloroform, xylene, m-cresol etc.
In yet another embodiment of the present invention, conductive composites of protonated polyaniline with polyvinyl chloride and ethylene vinyl acetate copolymer was prepared.
In yet another embodiment of the present invention, polyblend of polyaniline with ethylene vinyl acetate copolymer was prepared both by solution casting and by the in situ doping emulsion polymerisation in the presence of ethylene vinyl acetate copolymer. On doping the polyaniline with these dopants, it is observed that plastification also takes place simultaneously. Thus, these dopants act as plasticizing cum protonating agents. The plastification threshold of polyaniline occurs at dopant/polyaniline ratio of 0.2 to 0.4 and freestanding flexible films could be prepared-in the above ratio of dopant/polyaniline.
The conducting composites with plastics such polyvinyl chloride and elastomers such as ethylene vinyl acetate copolymer were prepared with a low percolation threshold. The polyblend of polyaniline doped with sulphonic acid of 3-pentadecyl anisole and polyvinyl chloride showed a conductivity of ca. 10xe2x88x923 S/cm for a 2% wt/wt of polyaniline, that is three orders of magnitude higher than that usually required for antistatic materials.